Grease composition and method for lubricating sliding part using the grease composition

Abstract

To provide a grease composition that does not deteriorate a contacting resin, particularly a contacting acetal resin, even under a high temperature condition.SOLUTION: The grease composition for a resin that can solve the above problem comprises: (A) a lubricant base oil; (B) a thickener; and (C) at least one selected from the group consisting of an organic molybdenum compound and a sulfur-based extreme pressure agent, wherein when the composition contains the sulfur-based extreme pressure agent, the content of the sulfur-based extreme pressure agent is 0.05 mass% or more to 2.5 mass% or less based on a total amount of the composition and zinc dialkyldithiophosphate is substantially free.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a grease composition. The present invention also relates to a method for lubricating a sliding part using this grease composition.

Background Art

[0002] Resin molded products are used as parts of various machines. Among them, molded products of polyacetal resin (acetal resin) have excellent properties in terms of mechanical properties and moldability. Due to such properties, molded products of acetal resin are widely used in home appliances and electric and electronic products.

[0003] Grease is mainly used for sliding bearings, rolling bearings (bearings), or sliding parts. The grease used is selected according to its usage conditions. In order to improve the lubricity and compatibility with materials of grease, various selections of base oil, thickener, and additive have been proposed. On the other hand, the friction characteristics vary depending on the conditions of the sliding part such as the material. Also, the grease used may deteriorate a specific material. Therefore, it is necessary to select a grease having an optimal composition in consideration of the material and the like.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 discloses a grease composition that can prevent contamination without causing lubrication failure and without the grease splashing and staying on surrounding equipment. Patent Document 2 discloses a grease composition that has low sliding resistance and can significantly reduce the power consumption of mechanical elements, particularly the power consumption during bearing rotation. However, in these documents, the suitability for resins has not been tested. Therefore, it was unclear whether they had suitability for resins. In particular, the sliding part often becomes hot. Therefore, there has been a demand for a grease composition that does not deteriorate the contacting resin even under high-temperature conditions.

Means for Solving the Problems

[0006] The present inventors have intensively studied a grease composition that does not deteriorate the contacting resin, particularly acetal resin, even under high-temperature conditions. And, when containing components (A) to (C) and a sulfur-based extreme pressure agent, the content of the sulfur-based extreme pressure agent is 0.05% by mass or less and 2.5% by mass or less based on the total amount of the composition, and by using a grease composition that does not substantially contain zinc dialkyldithiophosphate, they have found that the above problems can be solved and have completed the invention.

[0007] The present invention has been made based on such findings and is as follows. <1> (A) a lubricating base oil, (B) a thickener, and (C) at least one selected from the group consisting of an organic molybdenum compound and a sulfur-based extreme pressure agent, When containing a sulfur-based extreme pressure agent, the content of the sulfur-based extreme pressure agent is 0.05% by mass or more and 2.5% by mass or less based on the total amount of the composition, and a grease composition for resin that does not substantially contain zinc dialkyldithiophosphate. <2> The grease composition for resin according to <1>, wherein the resin is an acetal resin. <3> The grease composition for resin according to <1> or <2>, which contains an organic molybdenum compound and the content of the organic molybdenum compound is 0.05% by mass or more and 5% by mass or less based on the total amount of the composition. <4> The grease composition for resin according to any one of <1> to <3>, which contains both an organic molybdenum compound and a sulfur-based extreme pressure agent. <5> The grease composition for resin according to any one of <1> to <4>, wherein the thickener is a metal soap-based thickener. <6> The grease composition for resin according to any one of <1> to <5>, having a consistency of 265 or more and 475 or less. <7> (A) The content of the lubricating base oil is 50% by mass or more and 95% by mass or less based on the total amount of the composition, and (B) The content of the thickener is 2% by mass or more and 30% by mass or less based on the total amount of the composition. The grease composition for resin according to any one of <1> to <6>. <8> A lubrication method for a sliding part, wherein the grease composition according to any one of <1> to <7> is interposed in the sliding part. The present invention also relates to the following content. <1a> (A) Mineral oil, and (B) Lithium complex, and (C) A grease composition for resin containing both molybdenum dithiocarbamate and dioctyl polysulfide, not containing zinc dialkyldithiophosphate, wherein the kinematic viscosity of the mineral oil at 40 °C is 25 mm 2 / s or more and 70 mm 2 / s or less, the content of the lithium complex is 11% by mass or more and 20% by mass or less based on the total amount of the composition, the content of the dioctyl polysulfide is 0.1% by mass or more and 2.0% by mass or less based on the total amount of the composition, and the content of the molybdenum dithiocarbamate is 0.05% by mass or more and 5% by mass or less based on the total amount of the composition. <2a> The grease composition for resin according to <1a>, wherein the resin is an acetal resin. <3a> The grease composition for resin according to <1a> or <2a>, wherein the consistency is 265 or more and 475 or less. <4a> The grease composition for resin according to <1a> or <2a>, wherein the content of the mineral oil is 50% by mass or more and 95% by mass or less based on the total amount of the composition. <5a> The grease composition for resin according to <1a> or <2a>, wherein the content of zinc dialkyldithiophosphate is 1% by mass or less based on the total amount of the composition. <6a> The grease composition for resin according to <2a>, which is used for a member containing an acetal resin and a metal. <7a> The grease composition for resin according to <6a>, wherein the metal is copper. <8a> The grease composition for resin according to <1a> or <2a>, wherein when the resin is immersed in the grease composition for resin at 90°C or higher for 100 hours or more under high-temperature conditions, the mass increase of the resin is 0% or more and 0.20% or less. <9a> The grease composition for resin according to <8a>, wherein the high-temperature conditions refer to the conditions of immersing the resin in the grease composition for resin at 105°C for 168 hours.

Advantages of the Invention

[0008] According to the grease composition of the present invention, it is possible to provide a grease composition that does not deteriorate the contacting resin, particularly an acetal resin, even under high-temperature conditions.

Embodiments for Carrying Out the Invention

[0009] 〔Component (A): Lubricating base oil〕 As the lubricating base oil used in the present invention, either mineral oil or synthetic base oil can be used. The kinematic viscosity of the lubricating base oil at 40°C is not particularly limited, but from the viewpoint of safely preparing grease having excellent lubricity, it is preferably 10 mm 2 / s or more, more preferably 20 mm 2 / s or more, more preferably 25 mm 2 / s or more, preferably 700 mm 2 / s or less, more preferably 500 mm 2 / s or less, more preferably 70 mm 2 / s or less. Further, in one embodiment, the kinematic viscosity of the lubricating oil base oil at 40°C is preferably 10 mm 2 / s or more and 700 mm 2 / s or less, more preferably 20 mm 2 / s or more and 500 mm 2 / s or less, more preferably 25 mm 2 / s or more and 70 mm 2 / s or less. The viscosity index of the lubricating oil base oil at 40°C is not particularly limited, but from the viewpoint of preparing grease having excellent lubricity, it is preferably 95 or more and 250 or less, more preferably 95 or more and 150 or less. The viscosity index and kinematic viscosity at 40°C in this specification respectively mean the viscosity index and kinematic viscosity at 40°C measured in accordance with JIS K2283. The flash point of the lubricating oil base oil is not particularly limited, but from the viewpoint of safety, preferably the flash point is 150°C or higher.

[0010] In the present invention, it is preferable to use a hydrocarbon oil (such as mineral oil or synthetic base oil) as the lubricating oil base oil, and it is more preferable to use mineral oil. Examples of the mineral oil include a distillate obtained by atmospheric distillation of crude oil, or a distillate obtained by further vacuum distillation of this distillate, and a lubricating oil fraction refined by various refining processes. As the refining processes, hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, clay treatment, etc. can be appropriately combined. By treating these refining processes in an appropriate order in combination, a lubricating oil base oil usable in the present invention can be obtained. A mixture of a plurality of refined oils having different properties obtained by subjecting different crude oils or distillates to different combinations of refining processes can also be used.

[0011] As the synthetic base oil, a base material excellent in hydrolysis stability can be used. Examples of such base materials excellent in hydrolysis stability include polyolefins such as poly-α-olefins, polyesters, polyalkylene glycols, alkylbenzenes, alkylnaphthalenes, and GTL base oils. Among the synthetic base oils, poly-α-olefin is preferable in terms of availability, cost, viscosity characteristics, and compatibility with oxidation stability.

[0012] The lubricating oil base oil can be used alone as mineral oil or synthetic base oil, or a mixture of two or more. In the present invention, the lubricating oil base oil can contain only mineral oil, or can also contain other lubricating oil base oils. Specifically, in the grease composition of the present invention, the content of the mineral oil can be, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more based on the lubricating oil base oil. In the present invention, the content of the lubricating oil base oil is preferably 50% by mass or more, more preferably 60% by mass or more, preferably 95% by mass or less, and more preferably 90% by mass or less based on the total amount of the grease composition. Further, in one embodiment, it is preferably 50% by mass or more and 95% by mass or less, and more preferably 60% by mass or more and 90% by mass or less. When the content of the lubricating oil base oil is within the above range, a grease composition having a desired consistency can be easily prepared.

[0013] 〔Component (B): Thickener〕 The grease composition of the present invention contains at least one selected from the group consisting of metal soap-based thickeners and urea-based thickeners.

[0014] 〔Metal soap-based thickener〕 Examples of the metal soap - based thickeners include simple soaps and complex soaps. A simple soap is a metal soap obtained by saponifying a fatty acid or an oil and fat with an alkali metal hydroxide or an alkaline earth metal hydroxide. A complex soap is a compound obtained by combining, in addition to the fatty acid used in the simple soap, an organic acid with a different molecular structure for complexification. The fatty acid may be a fatty acid derivative having a hydroxy group or the like. The fatty acid may be an aliphatic carboxylic acid such as stearic acid or an aromatic carboxylic acid such as terephthalic acid. As the fatty acid, a monovalent or divalent aliphatic carboxylic acid, for example, an aliphatic carboxylic acid having 6 to 20 carbon atoms is used, and particularly preferably, a monovalent aliphatic carboxylic acid having 12 to 20 carbon atoms or a divalent aliphatic carboxylic acid having 6 to 14 carbon atoms is preferably used. As the fatty acid, a monovalent aliphatic carboxylic acid containing one hydroxy group is preferred. As the organic acid combined with the fatty acid in the complex soap, dibasic acids such as acetic acid, azelaic acid or sebacic acid, or benzoic acid and the like are suitable. As the metal of the metal soap - based thickener, alkali metals such as lithium and sodium, alkaline earth metals such as calcium, and amphoteric metals such as aluminum are used. Among these, alkali metals, particularly lithium, are preferably used. In the present invention, "6 to 20 carbon atoms" means having 6 or more and 20 or less carbon atoms.

[0015] The metal soap - based thickener may be used alone or in combination of two or more. The content of the metal soap - based thickener is, for example, preferably 2% by mass or more, more preferably 3% by mass or more, still more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, based on the total amount of the grease composition. Also, in one embodiment, the content of the metal soap - based thickener is preferably 2% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, still more preferably 10% by mass or more and 20% by mass or less.

[0016] 〔Urea - based thickener〕 As the urea-based thickener, for example, a diurea compound obtained by the reaction of a diisocyanate and a monoamine, or a polyurea compound obtained by the reaction of a diisocyanate and a monoamine or a diamine can be used.

[0017] A diisocyanate is a compound in which two hydrogens of a hydrocarbon are substituted with isocyanate groups. Preferred diisocyanates include phenylenediisocyanate, tolylene diisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate, octadecane diisocyanate, decane diisocyanate, or hexane diisocyanate. The hydrocarbon in the diisocyanate may be an acyclic hydrocarbon group or a cyclic hydrocarbon group, and may be an aromatic hydrocarbon group, an alicyclic hydrocarbon group, or an aliphatic hydrocarbon group. The number of carbon atoms is preferably 2 to 20, particularly preferably 4 to 18.

[0018] A monoamine is a compound having one amino group in one molecule. Preferred monoamines include octylamine, dodecylamine, hexadecylamine, stearylamine, oleylamine, aniline, p-toluidine, and cyclohexylamine. A diamine is a compound having two amino groups in one molecule. Preferred diamines include ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, phenylenediamine, tolylenediamine, xylenediamine, and diaminodiphenylmethane. The hydrocarbon group of the monoamine or diamine may be an acyclic hydrocarbon group or a cyclic hydrocarbon group, and may be an aromatic hydrocarbon group, an alicyclic hydrocarbon group, or an aliphatic hydrocarbon group. The number of carbon atoms is preferably 2 to 20, particularly preferably 4 to 18.

[0019] As the urea-based thickener, a diurea compound, particularly one having an aromatic hydrocarbon group as a diisocyanate, and further an alkylene diaryl diisocyanate such as methylene diphenyl diisocyanate are preferable. The number of carbon atoms is preferably 12 to 24. As the monoamine, an aromatic amine, an alicyclic amine or an aliphatic amine can be used, and a mixed amine obtained by mixing these can also be used.

[0020] The urea-based thickener may be used alone or in combination of two or more. The content of the urea-based thickener is, for example, preferably 2% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less based on the total amount of the grease composition. Further, in one embodiment, the content of the urea-based thickener is preferably 2% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, still more preferably 5% by mass or more and 20% by mass or less.

[0021] The grease composition of the present invention preferably contains a metal soap-based thickener, and more preferably contains a lithium complex soap-based thickener. The grease composition of the present invention may contain both a metal soap-based thickener and a urea-based thickener, but preferably contains only one of them.

[0022] 〔Component (C): At least one selected from the group consisting of an organic molybdenum compound and a sulfur-based extreme pressure agent〕 The grease composition of the present invention contains at least one selected from the group consisting of an organic molybdenum compound and a sulfur-based extreme pressure agent.

[0023] 〔Organic molybdenum compound〕 Examples of the organic molybdenum compound include molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and Mo amine complex. As the organic molybdenum compound, it is preferable to use molybdenum dithiocarbamate, and it is more preferable to use molybdenum dithiocarbamate represented by the following formula (1).

[0024] Formula (1): JPEG2025105700000001.jpg44160(In the formula, R1 to R4 may be the same or different and are each a hydrocarbon group having 1 to 30 carbon atoms, and X1 to X4 may be the same or different and are each S or O). Each of R1 to R4 is preferably a cycloalkyl group or a linear alkyl group, and particularly preferably a linear alkyl group. Further, each of R1 to R4 is preferably a linear alkyl group having 1 to 5 carbon atoms, and particularly preferably a linear alkyl group having 4 carbon atoms.

[0025] The content of the organic molybdenum compound is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, still more preferably 0.1% by mass or more, preferably 15% by mass or less, more preferably 10% by mass or less, still more preferably 5% by mass or less, and most preferably 3% by mass or less based on the total amount of the grease composition. Further, in one embodiment, the content of the organic molybdenum compound is preferably 0.01% by mass or more and 15% by mass or less, more preferably 0.05% by mass or more and 10% by mass or less, still more preferably 0.05% by mass or more and 5% by mass or less, and most preferably 0.1% by mass or more and 3% by mass or less. By setting the content of the organic molybdenum compound to be equal to or higher than the above lower limit value, the friction coefficient can be kept low. By containing the organic molybdenum compound at or below the above upper limit value, the production cost can be suppressed while obtaining a sufficient friction coefficient reduction effect. The molybdenum element content in the organic molybdenum compound is preferably 5% by mass or more and 40% by mass or less, and more preferably 5% by mass or more and 30% by mass or less based on the organic molybdenum compound.

[0026] 〔Sulfur-based extreme pressure agent〕 As sulfur-based extreme pressure agents, known sulfur-based extreme pressure agents such as sulfurized oils and fats, sulfurized fatty acids, sulfurized esters, sulfurized olefins, dihydrocarbyl (poly)sulfides, alkylthiocarbamoyl compounds, thioterpenoid compounds, dialkylthiodipropionate compounds, sulfurized mineral oils, zinc dithiocarbamate compounds, etc. can be used. These sulfur-based extreme pressure agents may be used alone or in combination of two or more.

[0027] Sulfurized oils and fats are products obtained by reacting sulfur or sulfur-containing compounds with oils and fats (lard oil, whale oil, vegetable oil, fish oil, etc.). The sulfur content in sulfurized oils and fats is not particularly limited, but is usually 5% by mass or more and 30% by mass or less.

[0028] As sulfurized fatty acids, products obtained by sulfurizing unsaturated fatty acids by any method can be used, and specifically, sulfurized oleic acid etc. can be exemplified. As sulfurized esters, products obtained by sulfurizing unsaturated fatty acid esters (for example, products obtained by reacting unsaturated fatty acids (such as oleic acid, linoleic acid, or fatty acids extracted from the above-mentioned animal and vegetable oils and fats) with various alcohols) by any method can be used, and specifically, methyl sulfurized oleate, octyl sulfurized rice bran fatty acid, etc. can be exemplified.

[0029] Examples of sulfurized olefins include compounds represented by the following general formula (2). This compound can be obtained by reacting an olefin having 2 to 15 carbon atoms or its dimer to tetramer with a sulfurizing agent such as sulfur or sulfur chloride. As the olefin, propylene, isobutene, diisobutene, etc. can be used.

[0030] Formula (2): R11-Sa-R12 (In formula (2), R11 represents an alkenyl group having 2 to 15 carbon atoms, R12 represents an alkyl group or alkenyl group having 2 to 15 carbon atoms, and a represents an integer of 1 to 8.)

[0031] Dihydrocarbyl (poly) sulfide is a compound represented by the following general formula (3). Here, when R13 and R14 are alkyl groups, it may be referred to as alkyl sulfide.

[0032] Formula (3): R13-Sb-R14 (In formula (3), R13 and R14 may be the same or different, and each independently represents an alkyl group having 1 to 20 carbon atoms (which may be linear or branched and may have a cyclic structure), an aryl group having 6 to 20 carbon atoms, an alkylaryl group having 7 to 20 carbon atoms, or an arylalkyl group having 7 to 20 carbon atoms, and b represents an integer from 1 to 8.)

[0033] Examples of the alkylthiocarbamoyl compound include compounds represented by the following general formula (4).

[0034] Formula (4): JPEG2025105700000002.jpg74144(In formula (4), R15 to R18 may be the same or different, and each independently represents an alkyl group having 1 to 20 carbon atoms, and c represents an integer from 1 to 8.)

[0035] Examples of the thioterpene compound include the reaction product of phosphorus pentasulfide and pinene. Examples of the dialkylthiodipropionate compound include dilauryl thiodipropionate, distearyl thiodipropionate, etc.

[0036] Sulfurized mineral oil is a substance obtained by dissolving elemental sulfur in mineral oil. The mineral oil used for sulfurized mineral oil is not particularly limited, but specifically, paraffinic mineral oil, naphthenic mineral oil, etc. purified by appropriately combining known purification treatments for the lubricating oil fraction obtained by subjecting crude oil to atmospheric distillation and vacuum distillation can be mentioned. Also, as the elemental sulfur, any form such as lump, powder, molten liquid, etc. may be used. The sulfur content in the sulfurized mineral oil is not particularly limited, but is usually 0.05% by mass or more and 1.0% by mass or less based on the total amount of the sulfurized mineral oil.

[0037] As the zinc dithiocarbamate compound, a compound represented by the following general formula (5) can be used.

[0038] Formula (5): JPEG2025105700000003.jpg54140 (In general formula (5), R19 to R22 may be the same or different and each independently represents a hydrocarbyl group having 1 or more carbon atoms.)

[0039] As the sulfur-based extreme pressure agent, it is preferable to use dihydrocarbyl(poly)sulfide represented by general formula (3), and a dialkyl polysulfide in which both R13 and R14 in general formula (3) are alkyl groups is more preferable, and dioctyl polysulfide is even more preferable.

[0040] When the sulfur-based extreme pressure agent is included, its content is 0.05% by mass or more and 2.5% by mass or less based on the total amount of the grease composition from the viewpoints of imparting extreme pressure properties and not deteriorating the resin. Further, the content of the sulfur-based extreme pressure agent is preferably 0.1% by mass or more, preferably 2.0% by mass or less, more preferably 1.5% by mass or less. Further, in one embodiment, it is preferably 0.05% by mass or more and 2.0% by mass or less, more preferably 0.1% by mass or more and 1.5% by mass or less.

[0041] The grease composition of the present invention preferably contains both an organic molybdenum compound and a sulfur-based extreme pressure agent. Note that organic molybdenum compounds such as molybdenum dithiocarbamate and molybdenum dithiophosphate contain sulfur molecules. Therefore, these organic molybdenum compounds also fall under the category of sulfur-based extreme pressure agents. Here, even when the organic molybdenum compound also falls under the category of sulfur-based extreme pressure agents, in the present invention, the organic molybdenum compound is not treated as a sulfur-based extreme pressure agent, and the content of the organic molybdenum compound is not added to the content of the sulfur-based extreme pressure agent. Further, "containing both" an organic molybdenum compound and a sulfur-based extreme pressure agent means containing, in addition to the organic molybdenum compound, a sulfur-based extreme pressure agent that does not contain molybdenum.

[0042] [Zinc dialkyldithiophosphate] In consideration of the effects on resins and metals (specifically copper), the grease composition of the present invention substantially does not contain zinc dialkyldithiophosphate (hereinafter sometimes referred to as ZnDTP). Zinc dialkyldithiophosphate is usually added to grease for purposes such as improving corrosion resistance, load-carrying capacity, and anti-wear properties. The inventors of the present invention discovered that adding zinc dialkyldithiophosphate in addition to sulfur-based extreme pressure agents and / or organomolybdenum compounds has an adverse effect on the resins and metals with which the grease comes into contact. As used herein, "substantially not contained" means that zinc dialkyldithiophosphate does not contain an amount that normally provides the expected improvements in corrosion resistance, load-carrying capacity, and anti-wear properties. As used herein, "substantially not contained" means that zinc dialkyldithiophosphate is contained in an amount of, for example, 1% by mass or less, preferably 0.1% by mass or less, more preferably 0.01% by mass or less, based on the grease composition. The grease composition of the present invention most preferably does not contain zinc dialkyldithiophosphate.

[0043] [Other additives] In addition to the above components, solid lubricants, antioxidants, rust preventives, corrosion inhibitors, etc., which are generally used in greases, can be appropriately added to the grease composition of the present invention as needed.

[0044] Examples of solid lubricants include graphite, graphite fluoride, melamine cyanurate, polytetrafluoroethylene, antimony sulfide, alkali (earth) metal borates, etc. When the grease composition contains a solid lubricant, its content may be 0.1% by mass or more and 20% by mass or less based on the total amount of the grease composition.

[0045] Examples of the antioxidant include phenolic compounds such as 2,6-di-t-butylphenol and 2,6-di-t-butyl-p-cresol, and amine compounds such as monobutylphenylmonooctylphenylamine, dialkyldiphenylamine, phenyl-α-naphthylamine, and p-alkylphenyl-α-naphthylamine. When the grease composition contains an antioxidant, its content may be 0.1% by mass or more and 10% by mass or less based on the total amount of the grease composition.

[0046] Examples of the rust preventive include amines, neutral or overbased petroleum-based or synthetic oil-based metal sulfonates, metal carboxylates, esters, phosphoric acid, phosphates, and the like. When the grease composition contains a rust preventive, its content may be 0.005% by mass or more and 5% by mass or less based on the total amount of the grease composition.

[0047] As the corrosion inhibitor, for example, known corrosion inhibitors such as benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, and imidazole-based compounds can be used. When the grease composition contains a corrosion inhibitor, its content may be 0.01% by mass or more and 10% by mass or less based on the total amount of the grease composition.

[0048] The grease composition of the present invention can be obtained by mixing other additives as required in addition to components (A) to (C) as essential components, stirring, and then passing through a roll mill or the like.

[0049] 〔Resin〕 As used herein, the term "resin" includes both natural resins and synthetic resins. Synthetic resins include general-purpose plastics (such as polyethylene, polystyrene, polypropylene, polyvinyl chloride, etc.) and engineering plastics. From the viewpoints of heat resistance and mechanical strength, preferred synthetic resins include polyamide resins, acetal resins, polycarbonate resins, polysulfone resins, polyphenylene sulfide resins, polyamideimide resins, polyetheretherketone resins, phenolic resins, polyester resins, epoxy resins, etc., and acetal resins are more preferred. Targets for using the grease composition of the present invention include sliding parts of transportation machines such as automobiles, railways, or airplanes, industrial machines such as machine tools, household electrical appliances such as washing machines, refrigerators, or vacuum cleaners, and precision machines such as watches or cameras. The grease composition of the present invention is preferably used for bearings, gears, sliding surfaces, belts, joints, cams, etc. containing resin materials included in these devices.

[0050] 〔Grease Composition〕 The consistency of the grease composition of the present invention is preferably 265 or more and 475 or less, more preferably 265 or more and 385 or less, and even more preferably 310 or more and 340 or less. The consistency in this specification means the worked consistency measured in accordance with JIS K2220. The specific measurement conditions are as follows. The sample is packed into a consistency measuring cup, kept at 25°C, and then mixed reciprocally 60 times in 1 minute using a specified mixer. Next, the excess sample is removed with a spatula, the surface of the sample is flattened, and then a specified cone is dropped into the sample for 5 seconds, and the value obtained by multiplying the penetrated depth (mm) by 10 is defined as the worked consistency.

[0051] The grease composition of the present invention has a special effect of not deteriorating the contacting resin, particularly acetal resin, even under high-temperature conditions. The high-temperature conditions are, for example, the conditions of immersing the resin in the grease composition at 90°C or higher for 100 hours or more, and more specifically, the conditions of 105°C for 168 hours. "Not deteriorating the resin" means that the mass change of the resin is extremely small. Specifically, when the resin is immersed in the grease composition under the above high-temperature conditions, it means that the mass increase of the resin is 0% or more and 0.20% or less. The grease composition of the present invention is also weakly reactive to metals (such as copper), which are materials other than resins, and has the effect of not deteriorating the metals. Therefore, the grease composition of the present invention may be encapsulated in a single member containing both a resin and a metal (such as copper). Further, embodiments in contact with materials other than metals (such as copper) and resins are not excluded.

Examples

[0052] Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited by the following examples. Unless otherwise specified, % indicates mass %.

[0053] Examples 1, 4, 6 to 8, 10, Reference Examples 1 to 4, Examples 4 to 10 and Comparative Examples 1 to 3 <Grease formulation> For each example and each comparative example, a test grease composition was prepared by blending a thickener, a base oil, and an additive at the blending ratios shown in Tables 1 and 2. The following evaluations were performed on the obtained test grease composition. The evaluation results are shown in Tables 1 and 2.

[0054] (1) Base oil · Mineral oil 1: Kinematic viscosity 36.8 mm 2 / s (40°C) · Mineral oil 2: Kinematic viscosity 86.6 mm 2 / s (40°C) · Mineral oil 3: Kinematic viscosity 22.7 mm 2 / s (40°C) The base oils were mixed at the mass ratios shown in Tables 1 and 2 to prepare a lubricating oil base oil. (2) Thickener · Urea - based thickener: Reaction product of diphenylmethane diisocyanate and cyclohexylamine · Lithium complex thickener: Reaction product of lithium 12 - hydroxystearate and azelaic acid (3) Additive As described in Tables 1 and 2, additives were added. The details of the additives are as follows. The blending amounts of the base oil (total), thickener, and additive are based on the total amount of the grease composition. · MoDTC Manufactured by ADEKA Corporation (Product name: Sakura Lub 515) · Dioctyl polysulfide Manufactured by DIC Corporation (Product name: DAILUBE GS440L) · ZnDTP1 Manufactured by Chevron Oronite Japan Corporation (Product name: OLOA5283) · ZnDTP2 Manufactured by Nippon Lubrizol Corporation (Product name: LUBRIZOL1095) · Other additives 2,6 - Di - t - butylphenol, dialkyldiphenylamine, benzotriazole - based compound, thiadiazole - based compound, tricresyl phosphate

[0055] <Evaluation> (1) Mass change of acetal resin Test pieces of acetal resin with a thickness of 2 mm, a length of 40 mm, and a width of 20 mm were manufactured, and each grease composition was applied to these test pieces. Each test piece coated with these grease compositions was heated under the conditions of 105 °C for 168 hours. After heating, the grease composition was removed, and the mass change of the test piece before and after heating was measured. Those with an increase of 0% to 0.2% were judged not to deteriorate the acetal resin.

[0056] (2) Extreme pressure property In accordance with ASTM D2596, the welding load (WL) was measured by a four - ball tester under the following conditions. If the welding load was 2452 N or more, it was judged to have extreme pressure property. · Rotation speed: 1800 rpm · Temperature: Room temperature · Test time: 10 seconds

[0057] (3) Blackening change of copper plate In accordance with JIS K 2220, the copper plate corrosion after being held in a constant temperature air bath at 100 °C for 24 hours was measured.

Table 1

Table 2

[0058] In each of the grease compositions of Example 1, 4, 6 to 8, 10, Comparative Examples 1 to 4, and Examples 4 to 10, the mass increase of the acetal resin was all between 0% and 0.2%, the extreme pressure value was greater than 2452 N, and no corrosion of the copper plate was confirmed. In Comparative Example 1 with the addition of ZnDTP1 and Comparative Example 2 with the addition of ZnDTP2, the mass of the acetal resin decreased and corrosion of the copper plate occurred. In Comparative Example 3 with the addition of 3% by mass of dioctyl polysulfide, the mass of the acetal resin increased by more than 2.0%.

Industrial applicability

[0059] According to the grease composition of the present invention, it is possible to provide a grease composition that does not deteriorate the contacting resin, particularly an acetal resin, even under high temperature conditions.

Claims

1. (A) Mineral oil, (B) Lithium complex, (C) A grease composition for resin containing both molybdenum dithiocarbamate and dioctyl polysulfide, and not containing zinc dialkyldithiophosphate, The kinematic viscosity of the mineral oil at 40 °C is 25 mm 2 / s or more and 70 mm 2 / s or less, and wherein the content of the lithium complex is 11% by mass or more and 20% by mass or less based on the total amount of the composition, the content of the dioctyl polysulfide is 0.1% by mass or more and 2.0% by mass or less based on the total amount of the composition, and the content of the molybdenum dithiocarbamate is 0.05% by mass or more and 5% by mass or less based on the total amount of the composition. A grease composition for resin.

2. The grease composition for resin according to claim 1, wherein the resin is an acetal resin.

3. The grease composition for resin according to claim 1 or claim 2, having a penetration of 265 or more and 475 or less.

4. The grease composition for resin according to claim 1 or claim 2, wherein the content of the mineral oil is 50% by mass or more and 95% by mass or less based on the total amount of the composition.

5. The grease composition for resin according to claim 1 or claim 2, wherein the content of the zinc dialkyldithiophosphate is 1% by mass or less based on the total amount of the composition.

6. The grease composition for resin according to claim 2, which is used for a member containing an acetal resin and a metal.

7. The grease composition for resin according to claim 6, wherein the metal is copper.

8. When the resin is immersed in the grease composition for resin at 90°C or higher for 100 hours or longer under high-temperature conditions, the mass increase of the resin is 0% or more and 0.20% or less. The grease composition for resin according to claim 1 or claim 2.

9. The grease composition for resin according to claim 8, wherein the high-temperature conditions refer to the conditions under which the resin is immersed in the grease composition for resin at 105°C for 168 hours.

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